Counter-terrorism officials conceded yesterday that lethal chemical devices they feared had been stored at an east London house raided on Friday may never have existed.

Confidence among officials appeared to be waning as searches at the address continued to yield no evidence of a plot for an attack with cyanide or other chemicals. A man was shot during the raid, adding to pressure on the authorities for answers about the accuracy of the intelligence that led them to send 250 officers to storm the man's family home at dawn.

Officials are not yet prepared to admit the intelligence was wrong. But there is diminishing optimism that it will be shown to wholly or even partially correct. Speaking of the feared chemical devices, one official said: "They might be elsewhere or never existed."

The raid, at 4am on Friday, was launched after MI5 received intelligence from an informant of the existence of a viable chemicial device at the property, which was to be used in an attack in Britain with the potential for substantial loss of life.

During the raid a 23-year-old Muslim man was shot, and he and his brother were arrested on suspicion of terrorism.

Scotland Yard said yesterday that searches at the property would continue for several days. Sources with responsibility for the security of the transport system, one of the most likely targets of a chemical device, say they have not been made aware the searches have produced any trace of a chemical device, either at the address in east London or elsewhere. "So far nothing from the search bears out the intelligence," said one source.

The Guardian has learned that over the weekend police intensified their planning for dealing with community anger if it turns out the intelligence was wrong.

Security and intelligence officials yesterday defended the decision to raid the house: "We have a duty of care to the general public, we can't do [police anti-terrorist] operations by halves," said one official.

A senior police source explained the police's dilemma: "In other crime you can take a risk to firm up the intelligence. The trouble with this new world of terrorism is you don't have the time, you can't firm up the intelligence to the point you like.

"The public may have to get used to this sort of incident, with the police having to be safe rather than sorry."

Anti-terrorism police yesterday began questioning the man shot in the raid, after his release from hospital. His lawyer named him as Mohammed Abdul Kahar, 23, who with his brother Abul Koyair, 20, protest their innocence and deny any link to Islamist extremism.

Mr Koyair's solicitor, Julian Young, denied media reports that his client had any criminal convictions. Lawyers for the men also denied a report that Mr Kahar had been shot by his brother after grappling with an armed police officer for his gun.

Mr Kahar's solicitor, Kate Roxburgh, said the 23-year-old Royal Mail worker had been shot in the upper right hand side of his chest, with the bullet exiting through his shoulder on an upwards trajectory. She said his brother had been standing behind Mr Kahar at the time.

Both solicitors said there had been no struggle before the shot was fired without warning, but Ms Roxburgh said Mr Kahar had grabbed the gun after he was shot fearing it would be fired again, leaving him with a burn to his hand from the hot barrel.